The invention relates to a hand held bar code scanning device. More specifically, the invention relates to a hand held bar code scanning device which has a manually operated sealed optical trigger switch.
Bar code reading instruments are used in a wide variety of applications. For example, bar code reading instruments are used to read UPC (universal product code) information off of products in supermarkets and are used for inventory control during manufacturing.
FIG. 1 illustrates a conventional bar code reading instrument in the form of a scan gun 100. The scan gun 100 generates a beam which exits the scan gun via a window 10. The beam reflects off of the bar code being read and the reflected beam is received in the scan gun through window 10. The operator initiates scanning by depressing a mechanical trigger 20. When mechanical trigger 20 is depressed, it pivots around a pivot 30 and a lever arm thereof activates a mechanical/electrical switch 40, which in turn sends an electrical trigger signal to scanning circuitry.
The detailed design of bar code reading instruments, including the scanning circuitry, is described in U.S. patent application Ser. No. 08/056,887, filed Apr. 2, 1993 by Chay La, and entitled "Non-Contact Actuated Trigger Apparatus for Bar Code Laser Scanner"; U.S. Pat. No. 5,258,604, which was issued to James Behrens et al. on Nov. 2, 1993 and is entitled "Bar Code Scanner"; U.S. Pat. No. 5,237,161, which was issued to Scott R. Grodevant on Aug. 17, 1993 and is entitled "System for Automatically Reading Symbols, Such as Bar Codes, on Objects Which are Placed in the Detection Zone of a Symbol Reading Unit, Such as a Bar Code Scanner"; U.S. Pat. No. 5,212,371, which was issued to John A. Boles et al. on May 18, 1993 and is entitled "Hand Held Bar Code Scanner with Improved Aiming Means"; U.S. Pat. No. 5,200,597, which was issued to Jay M. Eastman et al. on Apr. 6, 1993 and is entitled "Digitally Controlled System for Scanning and Reading Bar Codes"; and U.S. Pat. No. 5,019,698, which was issued to Jay M. Eastman et al. on May 28, 1991 and is entitled "Bar Code Reading System Having Electrical Power Conservation and Laser Radiation Power Limiting Means." The entire contents of this patent application and all five of these patents are incorporated herein by reference. This above-referenced application and these patents are assigned to PSC, Inc. (Webster, N.Y.), the assignee of the present application.
U.S. Pat. No. 5,250,790, which was issued to Boris Melitsky et al. on Oct. 5, 1993, entitled "Hand-Mounted Scanner with Automatic Manual Initiation of Reading Indicia"; U.S. Pat. No. 5,250,792, which was issued to Jerome Swartz et al. on Oct. 5, 1993, entitled "Portable Laser Diode Scanning Head"; and U.S. Pat. No. 4,593,186, which was issued to Jerome Swartz on Jun. 3, 1986, entitled "Portable Laser Scanning System and Scanning Methods," all assigned to Symbol Technologies, Inc. (Bohemia, N.Y.), disclose other conventional scanners.
The inventors have discovered that use of a mechanical trigger and a mechanical/electrical switch, such as disclosed in the above-identified patents, results in several disadvantages. Mechanical components are prone to failure due to dust and moisture which can enter the components. Static electricity, such as that created from walking on a rug with a scan gun, can enter the internals of the scan gun through gaps and mechanical joints and adversely affect electrical circuitry therein.
Because mechanical switches may create a spark, some (though decidedly not all) mechanical switches are not suitable for use in potentially explosive environments without complicated sealing arrangements. Mechanical/electrical switches generate output signals which are somewhat irregular and may suffer switch bounce effects and are thus less than ideal for use in conjunction with digital circuitry. Moreover, mechanical parts are subject to wear and thus degrade over time. In addition, repetitive operation of a mechanical switch can create stress in the fingers, hands, and wrists of the individual operating the scanner.